This application claims the priority of Austrian utility model application GM 507/2002, filed Jul. 29, 2002, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a tamping machine for tamping ballast underneath ties of a track.
U.S. Pat. No. 4,632,037 discloses a tamping machine having a machine frame extending in a longitudinal direction and supported on the track by two undercarriages for mobility in an operating direction. A sub-frame is arranged between the undercarriages and supported for mobility on the track by a further undercarriage having a unit motive drive. The sub-frame is connected to the machine frame by means of a frame support for displacement relative thereto in the longitudinal direction. A vertically adjustable tamping unit and track lifting unit are arranged on the sub-frame between the further undercarriage and the frame support. In a tamping machine of this type, there is no need to stop a major part of the overall mass of the tamping machine, each time a tie is to be tamped, and then to accelerate it again, as only the sub-frame, carrying the working units, is subjected to this stop-and-go procedure. The displacement of the sub-frame is effected, on the one hand, by a motive drive integrated in the undercarriage of the sub-frame, and, on the other hand, by means of a hydraulic cylinder connecting the machine frame and sub-frame to one another.
It would be desirable and advantageous to provide an improved tamping machine of the afore-described type, with which it is possible to achieve a better acceleration of the sub-frame.
According to one aspect of the present invention, a tamping machine for tamping ballast underneath ties of a track is provided which comprises a machine frame extending in a longitudinal direction and supported on the track by two undercarriages for mobility in an operating direction; and a sub-frame arranged between the said undercarriages and supported for mobility on the track by a further undercarriage comprising a unit motive drive, the sub-frame being connected to the machine frame by means of a frame support for displacement relative thereto in the longitudinal direction. A vertically adjustable tamping unit and a track lifting unit are arranged on the sub-frame between the further undercarriage and the frame support. An acceleration drive is provided for assisting the unit motive drive in displacing the sub-frame in the longitudinal direction, the acceleration drive being rigidly connected to the machine frame by means of a drive fastening and comprising a piston end including a bracing plunger provided for temporary application to the sub-frame, wherein a maximum stroke m of the acceleration drive is shorter than a maximum displacement path a of the sub-frame relative to the machine frame.
In a machine including an acceleration drive designed in this way, the latter has the effect of an impulse generator, used for providing optimum assistance of the acceleration and support of the starting motion of the sub-frame. After this initial acceleration phase, the further advance of the sub-frame is accomplished in an optimal manner exclusively by means of the motive drive which is integrated in the undercarriage of the sub-frame.
According to another aspect of the present invention, the acceleration drive provided for assisting the unit motive drive in displacing the sub-frame in the longitudinal direction is rigidly connected to the sub-frame by means of a drive fastening and comprises a piston end including a bracing plunger provided for temporary application to the machine frame, wherein a maximum stroke m of the acceleration drive is shorter than a maximum displacement path a of the sub-frame relative to the machine frame.